Disc drives store data in tracks that form concentric circles on discs containing a storage medium such as a magnetic material. Each track is broken down into various segments known as sectors that are indexed by the disc drive so as to be independently addressable. For each sector, one or more servo wedges must be included to guide a read/write head of the disc drive. The one or more servo wedges extend from the inner diameter of a given zone of the drive to the outer diameter of the zone and contain individual servo bursts that delineate track boundaries and that can be read by the head to produce a signal that indicates the head's position relative to the track boundary.
The servo wedges must be written onto the disc during the manufacturing process. One manner of doing so is to use a servo track writing mechanism. The servo track writing mechanism is a separate device that applies magnetic fields to the disc to add the servo bursts that form the servo wedges. However, the servo track writer can become inaccurate for relatively high track densities. Therefore, self-servowriting has been developed whereby the read/write head of the disc drive writes the servo bursts. This process is time-consuming because the read/write head of a disc drive generally cannot read and write at the same time and multiple revolutions of the disc are required for the servo wedges of a single track to be written. The multiple revolutions are required so that the head can read one previously written servo wedge including one or more bursts so as to stay on the correct track and then write another servo burst corresponding to another servo wedge of the same sector later in time.
Utilizing a head with an offset read element and write element allows the read element to read a servo wedge including one or more bursts from one track while the write element is positioned over another track. Once the disc has rotated to the appropriate place after reading the servo wedge, the write element can write a new servo wedge such as a servo burst for the track it resides above. This offset between the read and write elements thereby allows the servo wedges of a track to be written without seeking the head between a track having servo wedges previously written and the track currently being written for each switch between a read and write operation.
However, at least two revolutions are required for each track using conventional self-servowriting with the offset head because a servo pattern of multiple bursts forming the servo wedge must be written to the disc surface for each sector and be continuous from the outer diameter to the inner diameter. In a first revolution, a first servo wedge of a sector which acts as a track-following guide for propagation, is read from a first track. Also during this revolution but at a different time, the write element writes a second servo wedge, which is the guide used for track-following during normal operation and during propagation of the first wedge, on a second track spaced from the first track by the offset for each sector position as it passes by the head. In a second revolution, the first servo wedge is written for the second track so as to continue to act as a guide for propagation and the second servo wedge of the first track is then read for each sector position as it passes by the head to accurately track-follow while the first servo wedge is being written. With thousands of tracks per disc surface, each revolution required per track for servowriting adds a significant amount of time to the manufacturing process.
Accordingly there is a need for a method and disc drive that can reduce the amount of time necessary for propagating servo wedges onto the disc.